The lactoperoxidase system (LPS) is a well known antimicrobial system and is composed of lactoperoxidase, thiocyanate and hydrogen peroxide. The system occurs naturally in milk. Although the mechanism of action is not completely understood, it is postulated that the system catalyses the oxidation of thiocyanate to hypothiocyanate and that the active antimicrobial is hypothiocyanate. Although LPS is known to affect Gram negative organisms such as Salmonella, the effect has been shown to require 3 to 4 hours of contact.
European Patent Application, publication no. 0 252 051, assigned to EWOS aktieboieg, discloses that the addition of an acid to adjust the pH of the lactoperoxidase enzyme in the dry state to between 3.25 and 6, increases the storage stability of the enzyme. Acids such as hydrochloric acid, sulphuric acid, nitric acid, citric acid, acetic acid, formic acid and others as well as acidifying buffering systems as citric acid-citrate buffering systems, phosphoric acid-phosphate buffer systems, and others are suggested.
In PCT application, international publication no. WO 88/02600, Poulsen discloses a bactericidal composition composed of lactoperoxidase, thiocyanate and peroxide used for dental and wound treatment preparations. U.S. Pat. No. 4,320,116, assigned to Astra-Ewos AD, discloses a process for preparing foodstuffs; using such foodstuffs to treat bacterial infections in mammals; and pharmaceutical preparations containing an antibacterial system comprising a thiocyanate, a solid, water-soluble peroxide donor and lactoperoxidase. No mention is made in either specification of pH control or adjustment.
EP application, publication number 0 307 376, assigned to EWOS Aktiebolag, discloses a composition having a microbiocide effect and comprising iodine and lactoperoxidase, a peroxide donor and a pH adjusting agent in such an amount that the pH is 3.25-7.0 when lactoperoxidase is used and the pH is between 3.5 and 6, preferably 4.5-6.5, when horse radish peroxidase is used. The term pH adjusting agent is defined as, primarily, suitable buffer systems such as citric acid-citrate buffer, phosphoric acid-phosphate buffer and other suitable buffer systems which lock the pH within appropriate range.
U.S. Pat. No. 5,043,176, commonly assigned herein, discloses that an antimicrobial polypeptide such as nisin, a hypothiocyanate generating system and a buffering component capable of providing a pH between about 3 and about 5 provide a synergistic antimicrobial combination against Gram negative bacteria.
The synergistic antimicrobial composition of this invention has been found to be an effective cidal agent against the Gram negative organisms, such as Salmonella, in a much shorter time period than the lactoperoxidase system alone. As such it will be useful to eliminate surface contaminations of food products and as a disinfectant for food processing plants.